The present invention relates to a waveguide band-pass filter used for a microwave or milliwave and, more particularly, to a waveguide band-pass filter having a higher-order mode blocking function.
In order to obtain an optimal susceptance as a characteristic of a waveguide band-pass filter, a capacitive window for reducing an E-plane size, an inductive window for reducing an H-plane size, or an iris is conventionally used to set an optimal susceptance at a distance of .lambda.g/2.
Such a waveguide band-pass filter is used to transmit a signal of only a specific band, and the signal often includes a second-order harmonic wave of a fundamental wave as a spurious component.
In order to block the second-order harmonic wave as the spurious component in the conventional waveguide band-pass filter, a low-pass filter is connected to the waveguide band-pass filter. As a result, a circuit arrangement is complicated, and a compact, lightweight waveguide band-pass filter cannot be obtained.